The invention relates to a consumer control device, with a compressed air maintenance unit having the following components:
an electrically controllable proportional pressure regulating valve, having a supply input and a service output,
a device inlet, connectable or connected to an external compressed air source, connected via an inlet channel to the supply input of the proportional pressure regulating valve,
a device outlet connectable or connected to an external consumer device, connected via an outlet channel to the service output of the proportional pressure regulating valve,
sensor arrangement at least in the form of a flow sensor for measuring the air flow occurring in the inlet channel and/or outlet channel and an outlet pressure sensor for measuring the outlet pressure prevailing in the outlet channel,
an internal electronic control unit connected via a signal path to the proportional pressure regulating valve and with the sensor arrangement, configured, to generate an electrical pressure regulating signal for the proportional pressure regulating valve, as a function of the state values of the compressed air measured by the sensor arrangement                wherein the proportional pressure regulating valve can regulate the outlet pressure prevailing in the outlet channel at various levels as a function of the electrical pressure regulating signal applied to it, wherein it is operable both in a working mode regulating the outlet pressure to a working pressure value and a hold mode regulating the outlet pressure to a hold pressure that is lower than the working pressure value.        
The invention further relates to a method for controlling the compressed air supply of a consumer device by means of a consumer control device, in particular with a configuration corresponding to the type mentioned above.
A prior art configured and usable in the abovementioned way is known from EP 2 865 899 A1. Here it is a case of a consumer control device, having a compressed air maintenance unit, to the device output of which a consumer device to be supplied with compressed air can be connected. The compressed air maintenance unit unit is equipped with a proportional pressure regulating valve, which by means of an internal electronic control unit is variably controllable with an electrical pressure control signal, in order to provide on the output side a regulated outlet pressure. A flow sensor measures the air flow to the connected consumer device, while an outlet pressure sensor also present measures the outlet pressure of the compressed air supplied to the consumer device. In the known device the proportional pressure regulating valve is operated, as a function of the flow, either in a working mode or in a hold mode referred to as standby mode. In working mode, the connected consumer device is supplied with compressed air, wherein the level of the outlet pressure corresponds to a working pressure value necessary for correct operation of the connected consumer device. If the air flow drops below a specified shutdown flow threshold, the proportional pressure regulating valve is placed in hold mode, in which the outlet pressure is lowered to a reduced hold pressure value, resulting in an energy saving.
From EP 2 728 205 A2 a consumer control device is similarly known, but in this case instead of a proportional pressure regulating valve a shut-off valve configured as a 2/2-way valve is present. In a normal operational phase of the consumer control device the shut-off valve adopts a release position allowing an unimpeded passage of air. If under certain circumstances it is intended to avoid air consumption in the downstream external consumer device or in the in channel system leading to this consumer device, the shut-off valve can be switched to a shut-off position preventing a passage of air. This may in particular be the case if the connected consumer device is not operated for a long period.
In a consumer control device known from DE 10 2011 012 558 B3, instead of a proportional pressure regulating valve or a 2/2-shut-off valve, a 3/3-way valve is present, with the help of which a connected consumer device cannot just be isolated from an external compressed air source, but if necessary a consumer-side venting can be carried out.
DE 10 2006 007 103 A1 discloses a modular compressed air maintenance unit which has a plurality of unit modules which are arranged one after another in a row direction and are connected releasably to one another. At least two unit modules are fastened releasably to one another by a module connector which is placed between them, wherein the module connector has a through opening, via which the two unit modules are connected fluidically to one another. The module connector is equipped with at least one sensor device which is connected to the through opening and makes it possible to monitor state values of the flowing compressed air.
DE 20 2006 002 145 U1 describes a compressed air maintenance unit comprising a compressed air inlet and a compressed-air outlet, which has a plurality of adjacent modules which are connected to one another by fastening means. The module arrangement comprises a pressure booster device which is capable of raising the pressure of the supplied compressed air to a higher working pressure.